(1) Field of the Invention
The present invention relates generally to an overcurrent safety construction for a printed circuit board and, more specifically, to an overcurrent protector provided on the rear surface of a printed circuit board made up of a metal foil and low-melting point solder whereby the circuit elements and board suffers from no damage due to overcurrent flow.
(2) Description of the Prior Art
The conventional safety construction arranged on a printed circuit board was a metal conductor itself in a form of aluminum or copper patterned on the rear surface of the printed circuit board.
In more detail, the conductor serving as a safety construction has its width narrower than other portions of the conductor so that an overcurrent does not pass through the conductor because the conductor melts as soon as an overcurrent occurs.
However, such a conventional safety construction for a printed circuit board has a shortcoming: since the overcurrent protector uses the same material as other conductors in the printed circuit board and has a narrow part, the narrow part in the conductor is melted only when an overcurrent of higher than for example 50 A flows therethrough. Therefore, in the case when a current somewhat higher than an ordinary current in the printed circuit board (for example, about 10 A excessing the allowable current of an ordinary safety means) flows therethrough, such a conventional safety construction does not function before the body of the printed circuit board is burned out because it takes too long for the metal conductor of the safety construction to arrive at its melting point (for copper 1083.degree. C. and for aluminum 670.degree. C.).